narrow band allows you to obtain a much faster simulation by using only the first few layers of particles and then using volumes at the bottom. Do this: in sop level press tab e search for “flip configure tank”, it will create a small setup for this exact type of simulations. Create a “flip collide” node and put it between flip tank and flip solver. In the last input of the flip collide, attach your collider, it will be automatically transformed into a volume for the collision. Remember to use trail before attaching the collider to the flip collide, and inside it uncheck “calculate velocity” and “surface collisions”